linux-kernel - Re: [PATCH v2 3/5] drm/bridge: it6505: modify DP link auto training

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Message-ID: <pbcwdoxu3k4nvfn5vpfap52dczsaykewkzxvf5x5moqoeq4wn3@j3pxtx3cgokd>
Date: Mon, 31 Mar 2025 10:30:17 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
To: Hermes.Wu@....com.tw
Cc: andrzej.hajda@...el.com, neil.armstrong@...aro.org, rfoss@...nel.org,
        Laurent.pinchart@...asonboard.com, jonas@...boo.se,
        jernej.skrabec@...il.com, maarten.lankhorst@...ux.intel.com,
        mripard@...nel.org, tzimmermann@...e.de, airlied@...il.com,
        simona@...ll.ch, Pet.Weng@....com.tw, Kenneth.Hung@....com.tw,
        treapking@...omium.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 3/5] drm/bridge: it6505: modify DP link auto training

On Mon, Mar 31, 2025 at 02:31:30AM +0000, Hermes.Wu@....com.tw wrote:
> >-----Original Message-----
> >From: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com> 
> >Sent: Monday, March 31, 2025 2:44 AM
> >To: Hermes Wu (吳佳宏) <Hermes.Wu@....com.tw>
> >Cc: Andrzej Hajda <andrzej.hajda@...el.com>; Neil Armstrong <neil.armstrong@...aro.org>; Robert Foss <rfoss@...nel.org>; Laurent Pinchart <Laurent.pinchart@...asonboard.com>; Jonas Karlman <jonas@...boo.se>; Jernej Skrabec <jernej.skrabec@...il.com>; Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>; Maxime Ripard <mripard@...nel.org>; Thomas Zimmermann <tzimmermann@...e.de>; David Airlie <airlied@...il.com>; Simona Vetter <simona@...ll.ch>; Pet Weng (翁玉芬) <Pet.Weng@....com.tw>; Kenneth Hung (洪家倫) <Kenneth.Hung@....com.tw>; treapking@...omium.org; dri-devel@...ts.freedesktop.org; linux-kernel@...r.kernel.org
> >Subject: Re: [PATCH v2 3/5] drm/bridge: it6505: modify DP link auto training
> >
> >On Wed, Mar 26, 2025 at 01:34:15PM +0800, Hermes Wu via B4 Relay wrote:
> >> From: Hermes Wu <Hermes.wu@....com.tw>
> >> 
> >> IT6505 supports HW link training which will write DPCD and check 
> >> training status automatically.
> >> 
> >> In the case that driver set link rate at 2.7G and HW fail to training, 
> >> it will change link configuration and try 1.65G. And this will cause 
> >> INT_VID_FIFO_ERROR triggered when link clock is changed.
> >> 
> >> When video error occurs, video logic is reset and link training 
> >> restart, this will cause endless auto link training.
> >> 
> >> Modify link auto training with disable INT_VID_FIFO_ERROR to avoid 
> >> loop and check INT_LINK_TRAIN_FAIL event to abort wait training done.
> >> 
> >> Signed-off-by: Hermes Wu <Hermes.wu@....com.tw>
> >> ---
> >>  drivers/gpu/drm/bridge/ite-it6505.c | 38 
> >> +++++++++++++++++++++++++++----------
> >>  1 file changed, 28 insertions(+), 10 deletions(-)
> >> 
> >> diff --git a/drivers/gpu/drm/bridge/ite-it6505.c 
> >> b/drivers/gpu/drm/bridge/ite-it6505.c
> >> index 
> >> 0607f99446b37c82b41a376c2f4e10c7565d1b61..e0e13e737763fb801fd1cd803734
> >> a0d6ae1dd812 100644
> >> --- a/drivers/gpu/drm/bridge/ite-it6505.c
> >> +++ b/drivers/gpu/drm/bridge/ite-it6505.c
> >> @@ -1800,11 +1800,20 @@ static void it6505_link_training_setup(struct 
> >> it6505 *it6505)
> >>  
> >>  static bool it6505_link_start_auto_train(struct it6505 *it6505)  {
> >> -	int timeout = 500, link_training_state;
> >> +	int link_training_state;
> >>  	bool state = false;
> >>  	int int03;
> >> +	struct device *dev = it6505->dev;
> >> +	unsigned long timeout;
> >> +
> >> +	guard(mutex)(&it6505->aux_lock);
> >
> >Please don't mix functional changes and refactoring.
> >
> >> +	/* Disable FIFO error interrupt trigger  */
> >> +	/* to prevent training fail loop issue   */
> >> +	it6505_set_bits(it6505, INT_MASK_03, BIT(INT_VID_FIFO_ERROR), 0);
> >> +
> >> +	it6505_write(it6505, INT_STATUS_03,
> >> +		     BIT(INT_LINK_TRAIN_FAIL) | BIT(INT_VID_FIFO_ERROR));
> >>  
> >> -	mutex_lock(&it6505->aux_lock);
> >>  	it6505_set_bits(it6505, REG_TRAIN_CTRL0,
> >>  			FORCE_CR_DONE | FORCE_EQ_DONE, 0x00);
> >>  	/* reset link state machine and re start training*/ @@ -1812,32 
> >> +1821,41 @@ static bool it6505_link_start_auto_train(struct it6505 *it6505)
> >>  		     FORCE_RETRAIN | MANUAL_TRAIN);
> >>  	it6505_write(it6505, REG_TRAIN_CTRL1, AUTO_TRAIN);
> >>  
> >> -	while (timeout > 0) {
> >> +	timeout = jiffies + msecs_to_jiffies(100) + 1;
> >> +	for (;;) {
> >>  		usleep_range(1000, 2000);
> >>  		link_training_state = it6505_read(it6505, REG_LINK_TRAIN_STS);
> >>  		int03 = it6505_read(it6505, INT_STATUS_03);
> >>  		if (int03 & BIT(INT_LINK_TRAIN_FAIL)) {
> >> -			it6505_write(it6505, INT_STATUS_03,
> >> -				     BIT(INT_LINK_TRAIN_FAIL));
> >> -
> >>  			DRM_DEV_DEBUG_DRIVER(dev,
> >>  					     "INT_LINK_TRAIN_FAIL(%x)!",
> >>  					      int03);
> >>  
> >> +			/* Ignore INT_VID_FIFO_ERROR when auto training fail*/
> >> +			it6505_write(it6505, INT_STATUS_03,
> >> +				     BIT(INT_LINK_TRAIN_FAIL) |
> >> +				     BIT(INT_VID_FIFO_ERROR));
> >
> >Why can't it stay where it was?
> 
> Do you mean stay at original INT_LINK_TRAIN_FAIL clear and just add INT_VID_FIFO_ERROR?

Yes.

> 
> 

-- 
With best wishes
Dmitry